In 1981 the physicist Richard Feynman speculated about the possibility of “tiny computers obeying quantum mechanical laws.” He suggested that such a quantum computer might be the best way to simulate real-world quantum systems, a challenge that today is largely beyond the calculating power of even the fastest supercomputers. … Recent progress has renewed enthusiasm for finding avenues to build significantly more powerful quantum computers. Laboratory efforts in the United States and in Europe are under way using a number of technologies.